Line a 9x9 baking pan with foil, allowing foil to hang over the edge for easy removal. Spray foil with cooking spray. Place graham crackers on bottom of the pan, breaking to evenly fit. Sprinkle marshmallows evenly over graham crackers. Melt caramel and milk together in a microwave safe bowl for 1 minute. Stir and continue heating in 30 second intervals until melted. Pour caramel over the marshmallows and gently spread until evenly coated. The marshmallows will melt slightly, which is fine. Make sure to coat evenly so the caramel sticks to the graham crackers. Sprinkle chopped Butterfinger on top and press the candies into the caramel/marshmallow mix. Melt semi-sweet chocolate in a microwave safe bowl on high power in 30 second intervals until melted. Drizzle semi-sweet chocolate on top of Butterfinger. Chill in refrigerator for 1 hour or until set. Cut into bars when ready to serve.
NOTES: Store and serve bars at room temperature in an airtight container for up to a week.